Abstract:
Ayusman Sen, head of the Department of Chemistry at Penn State, makes tiny, metallic objects do something extraordinary -- he makes them swim. Sen's work is driven by catalysis, the chemical phenomenon whereby a substance accelerates a chemical reaction but emerges unchanged at the end of the process.

The chemical reaction upon which he and his team of students and colleagues focus their efforts is the well-known redox reaction, in which electrons and protons are broken away from their parent atoms and are pumped back and forth between substances, resulting in the liberation of energy during the process.

That energy manifests itself as an electrical gradient in the fluid surrounding a micro particle or nanomotor. Frequently, the motor is one of the group's two-micron-long platinum-gold nanorods. In most cases, the fluid starts out as a dilute solution of hydrogen peroxide which, upon being catalytically oxidized by the platinum tip of a nanorod, results in oxygen and also in electrons and protons that flow from bow to stern; electrons inside the rod; and an equal number of protons in the fluid along the outside of the rod. At the stern, the electrons and protons catalytically reduce hydrogen peroxide to water. The protons flowing from stem to stern function like paddles propelling the nanorod toward its platinum forward end, or if the nanorod is stationery, pumping water around it toward the aft end.